Field of the Invention
The present invention relates to a light signal transmitting apparatus having first and second light signal terminals and two optical fibers for coupling the first and second light signal terminals to transmit light signals in the opposite directions.
Description of the Prior Art
An example of this type of conventional light signal transmitting apparatus will be described below with reference to FIG. 1 of the accompanying drawings.
As shown in FIG. 1, there are provided links 31, 32 which serve as first and second light signal terminals. The two links 31, 32 are coupled with each other by two optical fibers 33, 34 through which light signals are transmitted in the opposite directions. The link 31 includes a laser diode 35 serving as an electro-optic converter and a photo-diode 36 serving as an opto-electro converter. The link 32 includes a laser diode 38 serving as an electro-optic converter and a photo-diode 37 serving as an opto-electro converter.
In the link 31, an electrical signal is supplied to the laser diode 35, in which it is converted into a laser light signal. This laser light signal is transmitted through the optical fiber 33 and received by the photo-diode 37 in the link 32, in which it is converted into an electrical signal. In the link 32, an electrical signal is supplied to the laser diode 38, in which it is converted into a laser light signal. This laser light signal is transmitted through the optical fiber 34 and received by the photo-diode 36 in the link 31, thereby being converted into an electrical signal.
When the conventional light signal transmitting apparatus uses a non-laser light emitting device, such as an LED (light emitting diode) or the like, a light emitted from such non-laser light emitting device cannot be modulated by a high speed electrical signal. Therefore, when the electrical signal is the high speed electrical signal, the laser light emitting device, such as the laser diode or the like, must be used. In the light signal transmitting apparatus, if an optical fiber through which a laser light is transmitted is disengaged from optical equipments or broken down, there is then the risk that a laser light is leaked to the outside to damage human eyes or the like.
If an intensity of the laser light transmitted through the optical fiber is set to be relatively low, even when the laser light is leaked to the outside, there is then no risk that the laser light thus leaked will hurt human eyes or the like. With the above arrangement, however, a transmission quality of the laser light is degraded with the result that the transmission distance of the laser light is reduced.